Patent application title: METHOD FOR MAKING A CURRENT-PERPENDICULAR-TO-THE-PLANE (CPP) MAGNETORESISTIVE (MR) SENSOR WITH AN ANTIPARALLEL FREE (APF) STRUCTURE FORMED OF AN ALLOY REQUIRING POST-DEPOSITION HIGH TEMPERATURE ANNEALING

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Abstract:

A method for making a current-perpendicular-to-the plane magnetoresistive
(CPP-MR) sensor with an antiparallel-free APF structure having the first
free layer (FL1) formed of an alloy, like a Heusler alloy, that requires
high-temperature or extended-time post-deposition annealing includes the
step of annealing the Heusler alloy material before deposition of the
antiparallel coupling layer (APC) of the APF structure. In a modification
to the method, a protection layer, for example, a layer of Ru, Ta, Ti,
Al, CoFe, CoFeB or NiFe, may deposited on the layer of Heusler alloy
material prior to annealing, and then etched away to expose the
underlying Heusler alloy layer as FL1.

Claims:

1. A method for making a magnetoresistive sensor having an antiparallel
free (APF) structure comprising: providing a substrate; depositing on the
substrate a layer of material selected from a Heusler alloy material and
a non-Heusler alloy material of the form
(CoyFe.sub.(100-y))100-z)Xz (where X is one or more of Ge,
Al, Si or Ga, y is between about 45 and 55 atomic percent, and z is
between about 20 and 40 atomic percent); annealing said selected Heusler
alloy material or non-Heusler alloy material to form a first free layer
(FL1); depositing on the FL1 layer an antiparallel coupling (APC) layer;
and depositing on the APC layer a second free layer (FL2) comprising a
ferromagnetic material other than a Heusler alloy.

2. The method of claim 1 further comprising, prior to said annealing,
depositing on the layer of said selected Heusler alloy material or
non-Heusler alloy material a nanolayer comprising a ferromagnetic
material other than a Heusler alloy, and wherein said annealing forms a
bilayer FL 1 comprising said selected Heusler alloy material or
non-Heusler alloy material and said nanolayer.

3. The method of claim 1 further comprising, after said annealing and
prior to depositing said APC layer, depositing on the layer of said
selected Heusler alloy material or non-Heusler alloy material a nanolayer
comprising a ferromagnetic material other than a Heusler alloy.

4. The method of claim 1 further comprising, prior to said annealing,
depositing on the layer said selected Heusler alloy material or
non-Heusler alloy material a protection layer; and, after annealing and
prior to depositing said APC layer, removing said protection layer.

6. The method of claim 1 wherein the layer of selected material is a
Heusler alloy and wherein annealing the Heusler alloy material forms a
first free layer (FL1) comprising a Heusler alloy layer selected from
Co2MnX (where X is one of Ge, Si, or Al), Co2FeZ (where Z is
one of Ge, Si, Al or Ga) and CoFexCr.sub.(1-x)Al (where x is between
0 and 1).

7. The method of claim 1 wherein the layer of selected material is the
non-Heusler alloy (CoyFe.sub.(100-y)).sub.(100-z)Gez (where y
is between about 45 and 55 atomic percent, and z is between about 20 and
40 atomic percent).

8. The method of claim 1 further comprising, prior to depositing said
selected Heusler alloy material or non-Heusler alloy material, depositing
on the substrate a layer of Mn-alloy material capable of becoming
antiferromagnetic and a ferromagnetic pinned layer in contact with said
Mn-alloy layer; and wherein said annealing improves the microstructure of
said Mn-alloy so as to form a Mn-alloy antiferromagnetic layer which
provides exchange biasing to said ferromagnetic pinned layer.

9. The method of claim 8 wherein said annealing is a first annealing step
at a first temperature and further comprising, after depositing said FL2,
performing a second annealing step at a temperature lower than said first
temperature.

10. The method of claim 8 further comprising, after depositing said layer
of Mn-alloy material and prior to depositing said selected Heusler alloy
material or non-Heusler alloy material, depositing a nonmagnetic spacer
layer, and wherein depositing said selected Heusler alloy material or
non-Heusler alloy material comprises depositing said selected Heusler
alloy material or non-Heusler alloy material on said spacer layer.

13. A method for making a magnetoresistive sensor having an antiparallel
free (APF) structure comprising: providing a substrate; depositing on the
substrate a layer of Mn-alloy material capable of becoming
antiferromagnetic; depositing on the Mn-alloy layer a ferromagnetic
pinned layer; depositing on the pinned layer a nonmagnetic spacer layer;
depositing on the spacer layer a layer of Heusler alloy material;
depositing on the layer of Heusler alloy material a nanolayer of a
ferromagnetic material other than a Heusler alloy material; annealing the
layer of Heusler alloy material to form a first free layer (FL1)
comprising a bilayer of a Heusler alloy layer selected from Co2MnX
(where X is one of Ge, Si, or Al), Co2FeZ (where Z is one of Ge, Si,
Al or Ga) and CoFexCr.sub.(1-x)Al (where x is between 0 and 1) and
said ferromagnetic nanolayer; depositing on said ferromagnetic nanolayer
of the FL1 an antiparallel coupling (APC) layer; and depositing on the
APC layer a second free layer (FL2) comprising a ferromagnetic material
other than a Heusler alloy; and wherein said annealing improves the
microstructure of said Mn-alloy so as to form a Mn-alloy
antiferromagnetic layer and exchange bias said ferromagnetic pinned
layer.

14. The method of claim 13 further comprising, prior to said annealing,
depositing on the nanolayer layer of the FL1 a protection layer; and,
after annealing and prior to depositing said APC layer, removing said
protection layer.

16. The method of claim 13 wherein said annealing is a first annealing
step at a first temperature and further comprising, after depositing said
FL2, performing a second annealing step at a temperature lower than said
first temperature.

19. The method of claim 13 wherein depositing a ferromagnetic pinned
layer comprises depositing an AP-pinned structure having a ferromagnetic
AP1 layer in contact with said Mn-alloy layer, a ferromagnetic reference
AP2 layer, and a nonmagnetic coupling layer between AP1 and AP2, and
wherein depositing said nonmagnetic spacer layer comprises depositing
said nonmagnetic spacer layer on the AP2 layer.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates generally to a
current-perpendicular-to-the-plane (CPP) magnetoresistive (MR) sensor
with an antiparallel free (APF) structure that has its first free layer
(FL1) formed of an alloy that requires high-temperature or extended-time
annealing, like a Heusler alloy, and more particularly to a method for
making the sensor.

[0003] 2. Background of the Invention

[0004] One type of conventional magnetoresistive (MR) sensor used as the
read head in magnetic recording disk drives is a "spin-valve" sensor
based on the giant magnetoresistance (GMR) effect. A GMR spin-valve
sensor has a stack of layers that includes two ferromagnetic layers
separated by a nonmagnetic electrically conductive spacer layer, which is
typically copper (Cu). One ferromagnetic layer adjacent the spacer layer
has its magnetization direction fixed, such as by being pinned by
exchange coupling with an adjacent antiferromagnetic layer, and is
referred to as the reference layer. The other ferromagnetic layer
adjacent the spacer layer has its magnetization direction free to rotate
in the presence of an external magnetic field and is referred to as the
free layer. With a sense current applied to the sensor, the rotation of
the free-layer magnetization relative to the reference-layer
magnetization due to the presence of an external magnetic field is
detectable as a change in electrical resistance. If the sense current is
directed perpendicularly through the planes of the layers in the sensor
stack, the sensor is referred to as current-perpendicular-to-the-plane
(CPP) sensor.

[0005] In addition to CPP-GMR read heads, another type of CPP sensor is a
magnetic tunnel junction sensor, also called a tunneling MR or TMR
sensor, in which the nonmagnetic spacer layer is a very thin nonmagnetic
tunnel barrier layer. In a CPP-TMR sensor the tunneling current
perpendicularly through the layers depends on the relative orientation of
the magnetizations in the two ferromagnetic layers. In a CPP-GMR read
head the nonmagnetic spacer layer is formed of an electrically conductive
material, typically a metal such as Cu or Ag. In a CPP-TMR read head the
nonmagnetic spacer layer is formed of an electrically insulating
material, such as TiO2, MgO or Al2O3.

[0006] In CPP MR sensors, it is desirable to operate the sensors at a high
bias or sense current density to maximize the signal and signal-to-noise
ratio (SNR). However, it is known that CPP MR sensors are susceptible to
current-induced noise and instability. The spin-polarized bias current
flows perpendicularly through the ferromagnetic layers and, if it is
above a critical current density, produces a spin-torque (ST) effect on
the local magnetization. This can produce fluctuations of the
magnetization, resulting in substantial low-frequency magnetic noise if
the sense current is too large. CPP MR sensors with an antiparallel free
(APF) structure have been shown to have a higher critical current
density, so that they are less susceptible to current-induced noise and
instability. An APF structure comprises a first free ferromagnetic layer
(FL1), second free ferromagnetic layer (FL2), and an antiparallel (AP)
coupling (APC) layer between FL1 and FL2. The APC layer couples FL1 and
FL2 together antiferromagnetically with the result that FL1 and FL2
maintain substantially antiparallel magnetization directions.

[0007] Heusler alloys, which are chemically ordered alloys like
Co2MnX (where X is one or more of Ge, Si, or Al) and Co2FeZ
(where Z is one or more of Ge, Si, Al or Ga), are known to have high
spin-polarization and result in an enhanced magnetoresistance and are
thus desirable materials to use in an APF structure. Heusler alloys
require significant post-deposition annealing to achieve chemical
ordering and high spin-polarization. Other materials whose
spin-polarization is annealing-dependent are non-Heusler alloys of the
form CoFeX (where X is one or more of Ge, Al, Si or Ga).

[0008] What is needed is a CPP MR sensor with an APF structure that
includes a Heusler alloy or a non-Heusler alloy that requires significant
annealing and a method for making the APF structure.

SUMMARY OF THE INVENTION

[0009] The invention relates to a method for making a CPP-MR sensor with
an antiparallel-free APF structure having the first free layer (FL1)
formed of an alloy, like a Heusler alloy, that requires significant
post-deposition annealing (greater than 250° C. or longer than 12
hours). The sensor layers, including the antiferromagnetic (AF) layer
which must be annealed, up through and including the spacer layer, are
deposited on the substrate. The material that will make up the Heusler
alloy is then sputter deposited on the spacer layer. A high-temperature
anneal is then performed before the deposition of the antiparallel
coupling (APC) layer. This results in the microstructural improvement
(ordering) of both the AF layer and the Heusler alloy which becomes FL1.
The APC layer is deposited on the Heusler alloy FL1 layer and the
non-Heusler alloy second free layer (FL2) is deposited on the APC layer.
In a modification to the method, a protection layer, for example, a layer
of Ru, Ta, Ti, Al, CoFe, CoFeB or NiFe, is deposited on the layer of
Heusler alloy material prior to annealing. The high-temperature anneal is
then performed with the protection layer covering the layer of Heusler
alloy material. The protection layer is etched away to expose the
underlying Heusler alloy layer as FL1.

[0010] In addition to Heusler alloys, certain non-Heusler alloys also
require significant post-deposition annealing and can be used in the
method of this invention in place of the Heusler alloys. These
non-Heusler alloys are of the form
(CoyFe.sub.(100-y)).sub.(100-z)Xz (where X is one or more of
Ge, Al, Si or Ga, y is between about 45 and 55 atomic percent, and z is
between about 20 and 40 atomic percent).

[0011] For a fuller understanding of the nature and advantages of the
present invention, reference should be made to the following detailed
description taken together with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic top view of a conventional magnetic recording
hard disk drive with the cover removed.

[0013] FIG. 2 is an enlarged end view of the slider and a section of the
disk taken in the direction 2-2 in FIG. 1.

[0014] FIG. 3 is a view in the direction 3-3 of FIG. 2 and shows the ends
of the read/write head as viewed from the disk.

[0015]FIG. 4 is a cross-sectional schematic view of a prior art CPP MR
read head having an antiparallel-free (APF) structure as the free layer
and showing the stack of layers located between the magnetic shield
layers.

[0016] FIG. 5 is a flow chart illustrating the method of this invention.

[0017] FIG. 6 is a flow chart illustrating a modification to the method
shown by the flow chart of FIG. 5.

[0018] FIG. 7 is a M-H loop for an APF structure made according to the
method shown in the flow chart of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The CPP magnetoresistive (MR) sensor made according to this
invention has application for use in a magnetic recording disk drive, the
operation of which will be briefly described with reference to FIGS. 1-3.
FIG. 1 is a block diagram of a conventional magnetic recording hard disk
drive. The disk drive includes a magnetic recording disk 12 and a rotary
voice coil motor (VCM) actuator 14 supported on a disk drive housing or
base 16. The disk 12 has a center of rotation 13 and is rotated in
direction 15 by a spindle motor (not shown) mounted to base 16. The
actuator 14 pivots about axis 17 and includes a rigid actuator arm 18. A
generally flexible suspension 20 includes a flexure element 23 and is
attached to the end of arm 18. A head carrier or air-bearing slider 22 is
attached to the flexure 23. A magnetic recording read/write head 24 is
formed on the trailing surface 25 of slider 22. The flexure 23 and
suspension 20 enable the slider to "pitch" and "roll" on an air-bearing
generated by the rotating disk 12. Typically, there are multiple disks
stacked on a hub that is rotated by the spindle motor, with a separate
slider and read/write head associated with each disk surface.

[0020] FIG. 2 is an enlarged end view of the slider 22 and a section of
the disk 12 taken in the direction 2-2 in FIG. 1. The slider 22 is
attached to flexure 23 and has an air-bearing surface (ABS) 27 facing the
disk 12 and a trailing surface 25 generally perpendicular to the ABS. The
ABS 27 causes the airflow from the rotating disk 12 to generate a bearing
of air that supports the slider 20 in very close proximity to or near
contact with the surface of disk 12. The read/write head 24 is formed on
the trailing surface 25 and is connected to the disk drive read/write
electronics by electrical connection to terminal pads 29 on the trailing
surface 25. As shown in the sectional view of FIG. 2, the disk 12 is a
patterned-media disk with discrete data tracks 50 spaced-apart in the
cross-track direction, one of which is shown as being aligned with
read/write head 24. The discrete data tracks 50 have a track width TW in
the cross-track direction and may be formed of continuous magnetizable
material in the circumferential direction, in which case the
patterned-media disk 12 is referred to as a discrete-track-media (DTM)
disk. Alternatively, the data tracks 50 may contain discrete data islands
spaced-apart along the tracks, in which case the patterned-media disk 12
is referred to as a bit-patterned-media (BPM) disk. The disk 12 may also
be a conventional continuous-media (CM) disk wherein the recording layer
is not patterned, but is a continuous layer of recording material. In a
CM disk the concentric data tracks with track width TW are created when
the write head writes on the continuous recording layer.

[0021] FIG. 3 is a view in the direction 3-3 of FIG. 2 and shows the ends
of read/write head 24 as viewed from the disk 12. The read/write head 24
is a series of thin films deposited and lithographically patterned on the
trailing surface 25 of slider 22. The write head includes a perpendicular
magnetic write pole (WP) and may also include trailing and/or side
shields (not shown). The CPP MR sensor or read head 100 is located
between two magnetic shields S1 and S2. The shields S1, S2 are formed of
magnetically permeable material and are electrically conductive so they
can function as the electrical leads to the read head 100. The shields
function to shield the read head 100 from recorded data bits that are
neighboring the data bit being read. Separate electrical leads may also
be used, in which case the read head 100 is formed in contact with layers
of electrically conducting lead material, such as tantalum, gold, or
copper, that are in contact with the shields S1, S2. FIG. 3 is not to
scale because of the difficulty in showing very small dimensions.
Typically each shield S1, S2 is several microns thick in the
along-the-track direction, as compared to the total thickness of the read
head 100 in the along-the-track direction, which may be in the range of
20 to 40 nm.

[0022]FIG. 4 is an enlarged sectional view showing the layers making up
sensor 100 as would be viewed from the disk. Sensor 100 is a CPP MR read
head comprising a stack of layers formed between the two magnetic shield
layers S1, S2 that are typically electroplated NiFe alloy films. The
shields S1, S2 are formed of electrically conductive material and thus
may also function as electrical leads for the sense current IS,
which is directed generally perpendicularly through the layers in the
sensor stack. Alternatively, separate electrical lead layers may be
formed between the shields S1, S2 and the sensor stack. The lower shield
S1 is typically polished by chemical-mechanical polishing (CMP) to
provide a smooth substrate for the growth of the sensor stack. This may
leave an oxide coating which can be removed with a mild etch just prior
to sensor deposition. The sensor layers include an antiparallel (AP)
pinned (AP-PINNED) structure, an antiparallel free (APF) structure, and a
nonmagnetic spacer layer 130 between the AP-PINNED and APF structures.

[0023] The pinned ferromagnetic layer in a CPP MR sensor may be a single
pinned layer or an antiparallel (AP) pinned structure like that shown in
FIG. 4. An AP-pinned structure has first (AP1) and second (AP2)
ferromagnetic layers separated by a nonmagnetic antiparallel coupling
(APC) layer with the magnetization directions of the two AP-pinned
ferromagnetic layers oriented substantially antiparallel. The AP2 layer,
which is in contact with the nonmagnetic APC layer on one side and the
sensor's electrically nonmagnetic spacer layer on the other side, is
typically referred to as the reference layer 120. The AP1 layer, which is
typically in contact with an antiferromagnetic or hard magnet pinning
layer on one side and the nonmagnetic APC layer on the other side, is
typically referred to as the pinned layer 122. Instead of being in
contact with a hard magnetic layer, AP1 by itself can be comprised of
hard magnetic material so that AP1 is in contact with an underlayer on
one side and the nonmagnetic APC layer on the other side. The AP-pinned
structure minimizes the net magnetostatic coupling between the
reference/pinned layers and the CPP MR free ferromagnetic layer. The
AP-pinned structure, also called a "laminated" pinned layer, and
sometimes called a synthetic antiferromagnet (SAF), is described in U.S.
Pat. No. 5,465,185.

[0024] The pinned layer in the CPP MR sensor in FIG. 4 is a well-known
AP-pinned structure with reference ferromagnetic layer 120 (AP2) and a
lower ferromagnetic layer 122 (AP1) that are antiferromagnetically
coupled across a nonmagnetic coupling layer. The nonmagnetic coupling
layer is depicted as antiparallel coupling (APC) layer 123. The APC layer
123 is typically Ru, Ir, Rh, Cr, Os or alloys thereof. The AP1 and AP2
layers are typically formed of crystalline CoFe or NiFe alloys, or a
multilayer of these materials, such as a CoFe/NiFe bilayer. The AP1 and
AP2 ferromagnetic layers have their respective magnetization directions
127, 121 oriented antiparallel. The AP1 layer 122 may have its
magnetization direction pinned by being exchange-coupled to an
antiferromagnetic (AF) layer 124 as shown in FIG. 4. The AF layer 124 is
typically one of the antiferromagnetic Mn alloys, e.g., PtMn, NiMn, FeMn,
IrMn, PdMn, PtPdMn or RhMn, which are known to provide relatively high
exchange-bias fields. Typically the Mn alloy material provides lower or
little exchange-biasing in the as-deposited state, but when annealed
provides stronger exchange-biasing of the pinned ferromagnetic layer 122.

[0025] Alternatively, the AP-pinned structure may be "self-pinned" or it
may be pinned by a hard magnetic layer such as Co100-xPtx or
Co100-x-yPtxCry (where x is about between 8 and 30 atomic
percent). Instead of being in contact with an antiferromagnetic pinning
layer, AP1 layer 122 by itself can be comprised of hard magnetic material
so that it is in contact with an underlayer on one side and the
nonmagnetic APC layer 123 on the other side. In a "self pinned" sensor
the AP1 and AP2 layer magnetization directions 127, 121 are typically set
generally perpendicular to the disk surface by magnetostriction and the
residual stress that exists within the fabricated sensor. It is desirable
that the AP1 and AP2 layers have similar moments. This assures that the
net magnetic moment of the AP-pinned structure is small so that
magnetostatic coupling to the APF structure is minimized and the
effective pinning field of the AF layer 124, which is approximately
inversely proportional to the net magnetization of the AP-pinned
structure, remains high. In the case of a hard magnet pinning layer, the
hard magnet pinning layer moment needs to be accounted for when balancing
the moments of AP1 and AP2 to minimize magnetostatic coupling to the free
layer.

[0026] The APF structure comprises a first free ferromagnetic layer 101
(FL1), second free ferromagnetic layer 102 (FL2), and an antiparallel
(AP) coupling (APC) layer 103. APC layer 103, such as a thin (between
about 4 Å and 10 Å) Ru film, couples FL1 and FL2 together
antiferromagnetically with the result that FL1 and FL2 maintain
substantially antiparallel magnetization directions in the quiescent
state, as shown by arrows 111a, 111b, respectively. The
antiferromagnetically-coupled FL1 and FL2 rotate substantially together
in the presence of a magnetic field, such as the magnetic fields from
data recorded in a magnetic recording medium. The net magnetic
moment/area of the APF structure (represented by the difference in
magnitudes of arrows 111a, 111b) is (M1*t1-M2*t2), where M1 and t1 are
the saturation magnetization and thickness, respectively, of FL1, and M2
and t2 are the saturation magnetization and thickness, respectively, of
FL2. Thus the thicknesses of FL1 and FL2 are chosen to obtain the desired
net free layer magnetic moment for the sensor.

[0027] A seed layer 125 may be located between the lower shield layer Si
and the AP-pinned structure. If AF layer 124 is used, the seed layer 125
enhances the growth of the AF layer 124. The seed layer 125 is typically
one or more layers of NiFeCr, NiFe, CoFe, CoFeB, CoHf, Ta, Cu or Ru. A
capping layer 112 is located between FL2 102 and the upper shield layer
S2. The capping layer 112 provides corrosion protection and may be a
single layer or multiple layers of different materials, such as Ru, Ta,
NiFe or Cu.

[0028] A ferromagnetic biasing layer 115, such as a CoPt or CoCrPt hard
magnetic bias layer, is also typically formed outside of the sensor stack
near the side edges of FL1 101. The biasing layer 115 is electrically
insulated from FL1 101 by insulating regions 116, which may be formed of
alumina, for example. The biasing layer 115 has a magnetization 117
generally parallel to the ABS and thus longitudinally biases the
magnetization 111a of the FL1 101. Thus in the absence of an external
magnetic field its magnetization 117 is parallel to the magnetization 111
of FL1 101. The ferromagnetic biasing layer 115 may be a hard magnetic
bias layer or a ferromagnetic layer that is exchange-coupled to an
antiferromagnetic layer.

[0029] In the presence of an external magnetic field in the range of
interest, i.e., magnetic fields from recorded data on the disk 12, the
magnetization directions 111a, 111b of the APF structure will rotate
together while the magnetization direction 121 of reference layer 120
will remain fixed and not rotate. Thus when a sense current IS is
applied from top shield S2 perpendicularly through the sensor stack to
bottom shield S1, the magnetic fields from the recorded data on the disk
will cause rotation of the magnetization directions 111a, 111b of the APF
structure relative to the reference-layer magnetization 121, which is
detectable as a change in electrical resistance.

[0030] The CPP MR sensor described above and illustrated in FIG. 4 may be
a CPP GMR sensors, in which case the nonmagnetic spacer layer 130 would
be formed of an electrically conducting material, typically a metal like
Cu, Au or Ag. Alternatively, the CPP MR sensor may be CPP tunneling MR
(CPP-TMR) sensor, in which case the nonmagnetic spacer layer 130 would be
a tunnel barrier formed of an electrically insulating material, like
TiO2, MgO or Al2O3.

[0031] The typical materials used for FL1 and FL2 are crystalline CoFe or
NiFe alloys, or a multilayer of these materials, such as a CoFe/NiFe
bilayer. Heusler alloys, i.e., metallic compounds having a Heusler alloy
crystal structure like Co2MnX, for example, have been proposed for
use in APF structures in CPP MR sensors, as described in U.S. Pat. No.
7,580,229 B2, assigned to the same assignee as this application. However,
it has been discovered, as part of the development of the method of this
invention, that the high-temperature annealing required to chemically
order the Heusler alloys can adversely affect the APF structure and thus
the magnetic performance of the sensor. Certain non-Heusler alloys of the
form CoFeX (where X is one or more of Ge, Al, Si or Ga) also require
post-deposition annealing and have been proposed for use in APF
structures. The annealing of these non-Heusler alloys will also likely
adversely affect the magnetic performance of the sensor.

[0032] In this invention, FL2 102 is formed of a typical ferromagnetic
material. However, FL1 101 is a Heusler alloy, i.e., a metallic compound
having a Heusler alloy crystal structure, of the type Co2MnX (where
X is one or more of Ge, Si, or Al), or Co2FeZ (where Z is one or
more of Ge, Si, Al or Ga) or (CoFexCr.sub.(1-x)Al (where x is
between 0 and 1). FL1 101 may be a single layer of a Heusler alloy or a
bilayer of a Heusler alloy first layer and a ferromagnetic nanolayer of a
material other than a Heusler alloy (like a CoFe or NiFe alloy having a
thickness between about 2 to 15 Å) between the Heusler alloy first
layer and the APC layer 103. These Heusler alloys are known to have high
spin-polarization and result in an enhanced MR in a CPP spin-valve
structure. These alloys require high-temperature annealing to produce the
required chemical ordering or high spin-polarization.

[0033] As an alternative to the above-described Heusler alloys, FL1 101
may be formed of a non-Heusler alloy of the form
(CoyFe.sub.(100-y)).sub.(100-z)Xz (where X is one or more of
Ge, Al, Si or Ga, y is between about 45 and 55 atomic percent, and z is
between about 20 and 40 atomic percent). This material also requires
significant post-deposition annealing. The preferred type of CoFeX
material is CoFeGe, which is described in U.S. Pat. No. 7,826,182 B2 for
use in CPP-MR sensors, including use in APF structures.

[0034] This invention is a method for making a CPP MR sensor like that
shown in FIG. 4 with an APF structure that has a Heusler alloy or a
non-Heusler CoFeX alloy as FL1 and a typical or conventional
ferromagnetic material, i.e., a non-Heusler alloy, as FL2. In the
conventional method for fabrication of a CPP MR sensor like that shown in
FIG. 4, all of the layers from seed layer 125 to capping layer 112 are
deposited as full films on S1, typically by sputter deposition. Then the
structure is annealed in a magnetic field (either in the deposition
chamber, or more commonly in an external annealing oven) to produce the
required exchange biasing effect of the AF layer 122, which is typically
PtMn or IrMn. The structure is then lithographically patterned and etched
to define the sensor track width (TW) on the ABS (see FIG. 3) and sensor
stripe height (SH), i.e., the height of the sensor orthogonal to the ABS.
However, it has been discovered, as part of the development of the method
of this invention, that if this conventional method is used with Heusler
alloy materials in an APF structure, the high-temperature annealing can
adversely affect the APF structure and thus the magnetic performance of
the sensor.

[0035] FIG. 5 illustrates the method of this invention as steps 300 to
355. The substrate with shield layer S1 is placed in the vacuum chamber
where the sputter deposition will be performed, and S1 is etched to
remove an oxide layer (step 300). The layers, including the AF layer
which must be annealed, up through and including the spacer layer are
deposited on S1 (step 305). The material that will make up the Heusler
alloy is sputter deposited on the spacer layer at step 310. For example,
if the Heusler alloy is to be chemically-ordered Co2MnSi, then a
single target or multiple targets with Co, Mn and Si are used to sputter
deposit a disordered layer containing the proper relative amounts of
these elements. The high-temperature anneal (step 320) is then performed
in the vacuum chamber before the deposition of the APC layer and is an
anneal at about 300-500 ° C. for about 5-30 minutes. This results
in the microstructural improvement (ordering) of both the AF layer and
the Heusler alloy FL1 layer. After cool-down at step 325, which may be
for about 5-30 minutes to reduce the temperature of the substrate to less
than about 100° C., the APC layer is deposited on the Heusler
alloy FL1 layer (step 330) and the non-Heusler alloy FL2 layer, e.g., a
CoFe alloy layer, is deposited on the APC layer (step 335). If the FL1
layer is to be a bilayer of a Heusler alloy first layer and a nanolayer
(like a CoFe alloy), then the optional nanolayer may be deposited (step
315) either before the high-temperature anneal step 320 or after the
cool-down step 325. After deposition of the capping layer (step 340), the
structure is removed from the vacuum chamber (step 345). An optional
low-temperature anneal (step 350) can then be performed at 200-250
° C. for 1-5 hours. The purpose of the optional low-temperature
anneal is to further anneal the AF layer to improve the exchange biasing
with the pinned layer (AP1 layer 122 in FIG. 4). The structure is then
patterned to form the sensor (step 355).

[0036] FIG. 6 illustrates a modification to the method of FIG. 5. This
modification will be explained for an example where the FL1 layer is to
be a bilayer of a Heusler alloy first layer and a nanolayer (like a CoFe
alloy), so the optional nanolayer is deposited on the layer of Heusler
material at step 315. Then at step 400 a protection layer is deposited on
the nanolayer. The protection layer may be, for example, a layer of Ru,
Ta, Ti, Al, CoFe, CoFeB or NiFe deposited to a thickness of about 30-100
Å. The substrate is then removed from the vacuum chamber (step 405)
and the high-temperature anneal (step 320) is performed with the
protection layer covering the nanolayer and the layer Heusler alloy
material below the nanolayer. After cool-down at step 325, the substrate
is then returned to a vacuum chamber (step 410) and the protection layer
is etched away, for example by Argon RF etching or ion milling, to expose
the underlying FL1 bilayer (step 415). The APC layer is deposited on the
FL1 bilayer (step 330) and the non-Heusler alloy FL2 layer is deposited
on the APC layer (step 335). After deposition of the capping layer (step
340), the structure is removed from the vacuum chamber (step 345). The
optional low-temperature anneal (step 350) can then be performed prior to
patterning the sensor (step 355).

[0037] FIG. 7 is a M-H loop for an APF structure made according to the
method of FIG. 6 and formed on a bilayer underlayer of 50 Å Ta/40
Å Ag. The FL1 bilayer is an 80 Å Co2MnSi Heusler alloy layer
with a 8 Å Co5oFe50 nanolayer. The APC layer is a 8 Å
Ru layer and the FL2 layer is a 10 Å Co50Fe50 layer. The
capping layer is a 70 Å Ru layer. The process used in this case was
according to FIG. 5, and thus no protection layer was used on the
nanolayer. The high-temperature annealing was done at 283° C. for
30 minutes. FIG. 7 shows strong antiparallel coupling of the
magnetizations of FL1 and FL2 at fields up to about 7500 Oe. At fields
about 8000 Oe, the antiparallel coupling is overcome and the
magnetizations of FL1 and FL2 become parallel. For the same APF structure
as described above with respect to FIG. 7, but where the FL1bilayer/Ru
APC layer/FL2 layer were annealed together under the same annealing
conditions, no significant antiparallel coupling was observed.

[0038] If the non-Heusler alloy
(CoyFe.sub.(100-y))100-z)Gez (where y is between about 45
and 55 atomic percent, and z is between about 20 and 40 atomic percent)
is used as FL1, it would have a typical thickness of about 30 to 70 Å
and would be annealed at about 250 to 350° C. for about 5 to 60
minutes.

[0039] While the present invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form and
detail may be made without departing from the spirit and scope of the
invention. Accordingly, the disclosed invention is to be considered
merely as illustrative and limited in scope only as specified in the
appended claims.